The process that generates the sun's energy is sustained nuclear fusion. Replicating this process in a controlled environment would yield an inexhaustible supply of energy, a commodity which is in short supply presently. For example, at the present rate of consumption, it is estimated that the world supply of oil will be exhausted within 100 years or less.
There is presently underway in the United States, and probably foreign countries, research efforts directed to processes for creating energy by controlled sustained nuclear fusion. It has been suggested that one way to achieve such nuclear fusion is to bombard a hydrocarbon foam target, or capsule, usually containing a deuterium-tritium (DT) fuel mixture, with a laser beam. The laser beam, at sufficiently high energy level, would cause a plasma envelope to form on the surface of the fuel mixture which would drive the capsule inward (imploding) to heat the fuel. Under appropriate conditions, the fuel will ignite in a thermonuclear burn, causing the fusion of deuterium and tritium to produce helium and give off energy.
The physics of the laser inertial confinement fusion, as this process is called, imposes several requirements on the design and material characteristics of the fuel and capsule that comprise the target of the laser beam.
By appropriate calculations and experimental efforts, it has been determined that optimum results will be obtained when a dense liquid or solid fuel is contained inside a capsule having near perfect spherical symmetry. The target capsule has a hollow core which provides a DT vapor region to serve as a spark plug when the fuel and vapor is compressed by the implosion.
In addition to the requirements of spherical configuration, it is also required that the capsule containing the fuel be porous, low in density and made with materials having a low atomic number. A capsule made of low density hydrocarbon foam is mostly empty space, and if porous or open celled, will act as a wick, soaking up fuel, thereby providing the maximum amount of fuel to fill the volume of the spherical capsule.
When liquid fuel is charged to the foam capsule, it becomes wet. For a wetted foam capsule, the internal structure must be sufficiently strong and the cells small enough so that capillary forces will support a liquid column about the height of the capsule diameter under the maximum acceleration that the capsule may undergo (.about.1000 g) during injection into a reactor at 1000 mls.
By calculation, it has been determined that each foam cell should be no more than about 1 .mu.m in diameter, that all cells must be linked to all others by passageways, and that the density of the foam be less than about 50 mg/cm.sup.3.